Stability of marine phytoplankton communities facing stress related to global change: Interactive effects of heat waves and turbidity

Abstract

A B S T R A C TAccording to climate models, coastal ecosystems will face an increased frequency of heat waves and increased turbidity due to terrestrial sediment run-off induced by increasing precipitation. Several studies have examined the effects of heat waves and turbidity separately, whereas this study analysed the individual effects of both stressors as well as their interaction, because stressors affect communities differently when acting in combination. Using a factorial experimental design, we simulated heat waves (22°C and 26°C compared to an 18°C control) and turbidity (sediment addition). The response of the phytoplankton community was analysed for the aggregate parameters biovolume and diversity index (H′), as well as for community composition. Heat waves had a significant negative effect on biovolume, whereas turbidity tended to affect biovolume positively. Repeated measures ANOVA revealed significant interactions of heat waves and turbidity for H′ and community composition. Strong heat waves (26°C) alleviated the otherwise positive effect of turbidity on H′, i.e. highest diversity remained in the turbid control. Diatoms gained dominance in the control and the 22°C heat wave treatment with Cylindrotheca closterium being the successful competitor. At 26°C this species was lost and small flagellates dominated the experimental communities. Future increases in heat wave intensity and frequency may thus induce major changes in phytoplankton community structure whereas algae might profit from increased turbidity as an additional source of nutrients.

Surviving Heatwaves: Thermal Experience Predicts Life and Death in a Southern Ocean Diatom

“…These findings are echoed by a large body of literature that concludes that environmental change is affecting marine phytoplankton, and will continue to do so in the future (Collins et al, 2020). Despite this, only a handful of studies have directly investigated the effect of MHWs on diatoms under controlled laboratory conditions (Bedolfe, 2015;Remy et al, 2017;Feijão et al, 2018). Microcosm experiments with marine phytoplankton communities exposed to simulated heatwaves and increased turbidity demonstrated that milder heatwaves (+4 • C from control) enhanced diatom growth rates, resulting in their dominance of the community, while in contrast, diatoms were completely absent in communities exposed to more intense heatwaves (+6 • C) (Remy et al, 2017).…”

“…Despite this, only a handful of studies have directly investigated the effect of MHWs on diatoms under controlled laboratory conditions (Bedolfe, 2015;Remy et al, 2017;Feijão et al, 2018). Microcosm experiments with marine phytoplankton communities exposed to simulated heatwaves and increased turbidity demonstrated that milder heatwaves (+4 • C from control) enhanced diatom growth rates, resulting in their dominance of the community, while in contrast, diatoms were completely absent in communities exposed to more intense heatwaves (+6 • C) (Remy et al, 2017). Feijão et al (2018) identified a number of physiological changes in the diatom Phaeodactylum tricornutum when exposed to heatwaves, including reduced photosynthetic efficiency and biomass production.…”

Phytoplankton mortality in a changing thermal seascape

“…Due to the increasing frequency of heat waves accompanying global warming in both terrestrial and aquatic systems (Frölicher et al, 2018; Ruthrof et al, 2018), thermally induced mortality plays a greater role in shaping community structure (Remy et al, 2017). Consequently, a large number of studies have focused on how thermal conditions (i.e.…”

Meta‐analysis of multiple driver effects on marine phytoplankton highlights modulating role ofpCO2

“…In our meta‐analysis, increasing temperature generally has a growth‐enhancing effect, especially for coccolithophores (Figure 2). In support, other studies found increasing temperatures to promote the development of earlier blooms and a different community structure in marine and freshwater phytoplankton (Boyd, 2019; De Senerpont Domis et al, 2014; Feng et al., 2009; Remy et al, 2017; Winder et al., 2012), where smaller phytoplankton groups including coccolithophores became more dominant (Coello‐Camba et al, 2014; Feng et al., 2009; Hare et al., 2007). The benefit of primary production from warming can, however, be compensated as community respiration might increase more strongly than community production (López‐Urrutia et al, 2006; Regaudie‐de Gioux & Duarte, 2012).…”